For me the issue isn't about birds or mice. It's about cats being allowed to roam freely when dogs are not. Some cats do dig up flowers, pee and poop in other people's yards and yup they kill the occasional bird and harm weaker cats. This isn't right or fair imo. My former outdoor cat was an expert bird catcher. I would suggest that GEOGRAPHY has loads to do with this.
But again all this is beside the point imo. If dogs can't roam free, why should cats be allowed to roam free?
Should cats be allowed to roam free on principle?